1. Field of the Invention
This invention relates to a method of detecting cylinder pressure in an internal combustion engine and more particularly to a method for detecting the maximum cylinder pressure as well as, if desired, the crankshaft angle at which the maximum cylinder pressure occurred.
2. Description of the Prior Art
Recent years have seen extensive adoption of methods for detecting cylinder combustion pressure in internal combustion engines and for using the detected values to control the ignition timing and other operating parameters of the engine. For the required determination of the combustion pressure, and more specifically for the determination of the maximum cylinder pressure (Pmax), it has been the practice to employ a method as disclosed in Japanese Patent Publication No. 59(1984)-2796 in which a maximum pressure detection circuit is constituted using an operational amplifier, a capacitor and the like, the outputs of a pressure sensor are added and input to the detection circuit, whereby the maximum pressure value is determined, and the determined value is stored at the capacitor. Further, for detecting the crankshaft angle at which the maximum pressure was reached, i.e. the maximum cylinder pressure angle .theta.pmax, there has conventionally been used a method such as that disclosed in Japanese Patent Publication No. 58(1983)-33394 in which the output of a pressure sensor is differentiated using a differentiation circuit and the result of the differentiation is applied to a comparison circuit for comparison with a predetermined value. However, as these prior art methods both rely on analog circuits for the detection, they are not totally satisfactory as regards accuracy or as regards tracking performance during highspeed engine operation. Another disadvantage of the conventional methods is that they require complicated circuitry.
As prior art technology aimed at overcoming the shortcomings of the aforesaid methods there can be noted Japanese Unexamined Patent Publication No. 57(1982)-173565 which relates to a method of using an A/D converter to A/D-convert the output of a cylinder pressure sensor once per a prescribed angle of crankshaft rotation and defining the crankshaft angle at the time the converted value reached maximum as the maximum cylinder pressure angle .theta.pmax. Although this method discloses methods for detecting the cylinder pressure and determining the maximum pressure value and the crankshaft angle at which the maximum pressure value occurs, it is incapable of simultaneously determining the presence or absence of knocking on the basis of the detected cylinder pressure and in this respect leaves much to be desired.